The present invention relates generally to air sampling and, more particularly, to portable air sampling systems and methods.
Personal air sampling devices can be used to determine the exposure of individuals to various airborne particles and contaminants over a period of time. For example, U.S. Pat. No. 4,721,517 to Cloutier and U.S. Pat. No. 5,119,682 to Bellinger each describe sampling devices configured to be worn by an individual and to obtain air samples within the breathing zone of the wearer. Sampled air is pumped through a filter which retains any airborne particles and/or contaminants. Subsequently, the filter can be weighed or subjected to other types of analysis in order to determine the nature of the collected particles and/or contaminants.
Air flow requirements for air sampling are conventionally based on the expected concentration of airborne particles, and the ability to measure and analyze the particles collected. Collection of too much particulate material can clog a filter and can cause a sampling flow rate to drop below acceptable levels. Sampling pumps for personal sampling systems conventionally operate at a fixed flow rate and with size-selective sampling inlets. Sampling periods are conventionally based upon the amount of particulate material collected. For example, shorter sampling periods may be used within environments having a higher average concentration of airborne particles.
In order to reduce inconvenience to a wearer, conventional personal air sampling devices typically are designed to be as small and as lightweight as possible. To facilitate portability, personal air sampling devices are conventionally battery powered. However, batteries may have a limited lifetime which can result in sampling periods that are not long enough to obtain a satisfactory air sample. In order to extend air sampling periods, intermittent air sampling can be performed wherein a sampling pump is operated intermittently, creating xe2x80x9cONxe2x80x9d periods and xe2x80x9cOFFxe2x80x9d periods. (See, for example, U.S. Pat. No. 5,201,231 to Smith and U.S. Pat. No. 4,080,832 to Moody et al.). Intermittent air sampling can extend battery life so that air sampling can be extended over a longer time period than achievable via continuous air sampling. Intermittent air sampling also facilitates obtaining representative aerosol samples over an extended period of time without xe2x80x9cblindingxe2x80x9d a filter by collecting too much particulate matter.
It would be valuable to independently verify that an air sampling device was worn by an individual during a time period designated for sampling (i.e., an ON period during intermittent operation). Unfortunately, conventional personal air sampling devices designed for intermittent operation may not provide an accurate way of ensuring that an individual is wearing a device during an ON period. Also, it would be valuable to know the level of physical activity of the wearer of an air sampling device during sampling because an inhaled dose of airborne particles may be a function of breathing rate as well as of sampling time.
It is known to sample air in proportion to the actual respiration of an individual. For example, in U.S. Pat. No. 4,183,247 to Allen et al., a sampling pump is activated by the expansion and contraction of an individual""s thoracic cavity during respiration. In addition, it is known to sample air in proportion to the pulmonary output of an individual. For example, U.S. Pat. No. 4,589,292 to Delhaye et al. describes a process and device for sampling ambient air in proximity of the respiratory track of an individual wherein a sampling pump is piloted by a signal indicating the individual""s cardiac rhythm, such as from the pulsed flow of blood in an ear lobe of the individual. Unfortunately, existing methods of monitoring physical activity of a person are somewhat personally intrusive and complex.
In view of the above, it is therefore an object of the present invention to provide personal air sampling devices that can operate autonomously over extended periods of time without inconvenience to the wearer.
It is another object of the present invention to provide personal air sampling devices that can monitor various air sampling system performance criteria.
It is another object of the present invention to provide personal air sampling devices that can verify that a device was worn properly by an individual during sampling.
It is another object of the present invention to provide a way of monitoring the physical activity of a person that can be less complex and personally intrusive.
These and other objects of the present invention are provided by portable air sampling apparatus and methods for sampling air in the breathing zone of a person over extended periods of time, wherein both air sampling performance and physical activity of the person can be continuously monitored. Air sampling methods according to the present invention include passively sampling air from the breathing zone of a person, and/or intermittently sampling air from the breathing zone of a person by drawing the air through a filter via a sampling pump. Pressure drop across the filter and the temperature of the air flowing through the filter can be continuously measured and recorded in a data logger. Other pump performance characteristics can be measured, as well. For example, voltage across a power supply that provides electric power to a pump motor can be continuously monitored. In addition, physical activity levels of a person wearing the air sampling device can be monitored easily and non-intrusively by measuring changes in electrical capacitance of a transducer maintained in close proximity to the person, or through the use of an accelerometer chip, motion switch, or light sensor.
According to an embodiment of the present invention, a small, lightweight pack, such as a fanny pack or a pack that can fit within a pocket of an article of clothing, can be configured to house various air sampling and activity monitoring components. One or more filter devices can be mounted on the outside of the pack to sample air in the breathing zone of the person. Each filter device may include a housing having an air inlet, an air outlet, and a filter element disposed within the housing. A filter element is configured to retain particles entrained within air flowing therethrough.
A sampling pump disposed within the pack, is in fluid communication with the filter device air outlet. The sampling pump is configured to draw a predetermined volume of air from the breathing zone of the wearer into the filter device and through the filter element. A timing circuit is provided with the pump for intermittently activating the sampling pump to draw the predetermined volume of air through the filter element at predetermined intervals.
Also included within the pack are various systems for monitoring air sampling system performance. For example, pressure drop across the filter and the temperature of air passing through the filter are continuously monitored and recorded in a data logger. In addition, voltage across a pump motor power supply can also be monitored on a continuous basis.
Also included within the pack is an activity monitoring system for monitoring the physical activity of the person wearing the pack. Activity can be monitored via changes in capacitance via capacitor plates, via one or more accelerometer chips, via one or more motion switches, or via one or more light switches. Information about physical activity are recorded in the data logger.
According to an embodiment of the present invention, an apparatus can intermittently pump air through a filter mechanism, can perform real-time logging of system performance, and can directly measure the activity levels of an individual wearing the system. The present invention is advantageous because the air sampling system is designed to be lightweight and convenient for a person to wear. Furthermore, intermittent air sampling includes a pattern of ON and OFF pump operation periods that can extend battery life so that a longer sampling period can be obtained than with continuous pump operation. Intermittent sampling can also make it possible to obtain representative air samples over an extended period of time with a reduced risk of clogging the filter with too much particulate material.
According to another embodiment of the present invention, a portable apparatus configured to be worn by a person, includes an air sampling system that samples air from a breathing zone of a person wearing the portable apparatus, a physical activity monitor that monitors physical activity of the person wearing the portable apparatus, and a data logger in communication with the physical activity monitor. The air sampling system may be a passive air sampling system or an active air sampling system, or a combination of passive and active air sampling systems. The portable apparatus may include an input device that communicates with the data logger and that allows a user to record information about his or her personal activities in the data logger. Preferably, the input device includes a keypad, and/or a user interface configured to receive user-provided data. The portable apparatus may also include a receiver in communication with the data logger that can receive data from remotely located communications devices, such as a Global Positioning System (GPS) receiver. The portable apparatus may also include a transmitter in communication with the data logger that can transmit data from the data logger to remotely located communications devices. The portable apparatus may also utilize Bluetooth wireless technology such that the data logger can communicate with various stationary devices located nearby. The portable apparatus may also include a system that measures airborne contaminants in real time.